As compounds having hexaazaisowurtzitane skeletons, various arylmethyl group-containing hexaazaisowurtzitane derivatives are known which are obtained by condensation of arylmethylamines and glyoxal (J. Org. Chem., vol. 55, 1,459-1,466, 1990). Tetraacetyldibenzylhexaazaisowurtzitane is known as an acyl group-containing hexaazaisowurtzitane compound and is reported to be a precursor of hexanitrohexaazaisowurtzitane which is a material for explosives (The Militarily Critical Technologies List, Office of the Under Secretary of Defense for Acquisition, 12-22, October 1992 and Tetrahedron, Vol. 51, No. 16, 4711-4722, 1995). Further, there are known ethyl group-containing hexaazaisowurtzitane derivatives such as tetraacetyl-diethylhexaazaisowurtzitane and the like (Tetrahedron, Vol. 51, No. 16, 4711-4722, 1995) and there are also known trimethylsilylethyloxycarbonyl group-containing hexaazaisowurtzitane derivatives (JP-A-6-321962). There are known benzyl and/or ethyl group-containing hexaazaisowurtzitane derivatives other than the above-mentioned tetraacetyldibenzylhexaazaisowurtzitane, tetraacetyldiethylhexaazaisowurtzitane.
The above-mentioned hexaazaisowurtzitane derivatives having acyl groups easily substitutable with nitro groups are useful as precursors of polynitrohexaazaisowurtzitane derivatives for high-performance explosives; however, use of the above-mentioned derivatives as precursors of the nitro compounds has problems. For example, since by-products such as nitrated aromatic compounds are produced in nitration of the benzyl group-containing hexaazaisowurtzitane derivatives, it is complicated to isolate and purify therefrom hexanitrohexaazaisowurtzitane, the target compound of the present invention. On the other hand, hydrochloric acid, i.e., a strong acid, which is produced during preparation of trimethylsilylethyloxycarbonyl group-containing hexaazaisowurtzitaines, causes the decomposition of hexabenzylhexaazaisowurtzitane that is the starting material in the process. It is reported that hexanitrohexaazaisowurtzitane is obtained by nitration of the tetraacetyldibenzylhexaazaisowurtzitane, but no detailed description is found on its method of preparation (Tetrahedron, vol. 51, No. 16, 4,711-4,722, 1995). It is further reported to be difficult to prepare hexanitrohexaazaisowurtzitane by nitration of tetraacetyldiethylhexaazaisowurtzitane (Tetrahedron, vol. 51, No. 16, 4,711-4,722, 1995).
Therefore, it has been long desired to develop a process for preparing hexanitrohexaazaisowurtzitane in a high yield by use of an acyl group-containing hexaazaisowurtzitane derivative. It is also an object of the present invention to prepare hexanitrohexaazaisowurtzitane in a high yield by use of hexaazaisowurtzitane derivatives.